Michael Phelps suffered his first big reverse when he trailed home in seventh in the final of the 100 metres freestyle at the US Swimming Championships in California.

Phelps, who ended a near two-year retirement in April, was racing in his fourth meet since returning to the sport with fans looking forward to another big clash with Olympic Games rival Ryan Lochte.

The 29-year-old, who has 18 Olympic golds in his collection, needed to finish in the top four to secure a place in the Pan Pacific Championships on the Gold Coast in Australia later this month but he made a mess of his halfway turn and was never able to recover.

When I literally took a couple kicks and I barely passed the flags, I knew there was very little chance that I was going to run anybody down.

Michael Phelps

And it was London 2012 champion Nathan Adrian who eventually outshone both of them, winning in 48.31 seconds ahead of Lochte, who has a collection of 11 Olympic medals, five of them golds.

"When I literally took a couple kicks and I barely passed the flags, I knew there was very little chance that I was going to run anybody down," Phelps said.

"It just kind of stinks that I missed the first wall."

But Phelps still has three chances to make the United States team for the August 21-25 event, with further races coming up in the 100 metres butterfly, 100 metres backstroke and 200 metres individual medley.

"I'm just trying to get a spot on the team and go from there," Phelps added. "I am ready to have a day off and get ready for the 100m fly."